Tachometer jewel frame and drive shaft retainer



E. F. BACON June 14, 1932.

TACHOMETER JEWEL FRAME AND DRIVE SEAFT RETAINER Filed. Feb. 16, 1929.

Patented June 14, 1932 UNITED STATES PATENT oFF-ICE ELBRIDG'E F. "BACON,T FLINT, MICHIGAN, ASSIGNOB TO A C SPARK 'IPLUG COMPANY,

OF FLINT, MICHIGAN, A COMPANY OF MICHIGAN TACHOMETER JEWEL FRAME ANDDRIV-E SHAFT ZR JEITJZHNER Application filed February 16, I929..Serial'No. 340 633.

This invention relates to tachometer-s.

An object of the invention is to improye the construction of such aninstrument in order to secure accuracy of its readings.

5 Another and related object is to provide an improved means forsecuring the parts together and securing the instrument to its support.

Another object is to so constr'uctthe instrum ment as to provideagreater range of adj ustment-s for the hair spring and also to renderthe hair spring and adjacent parts more accessible. v

j Still another object is to improve the speed 15 disc so as to preventwarping and to obtain a more uniform'pull .upon the disc. v I

Other objects and advantages will be .understood from the followingdescription:

In the drawing:

Figure 1 is a vertical front elevation of the instrument with the bezelremoved and the dial broken away to show the internalmechanism.

'Figuref2 is a cross section substantially on 25 line 2-2 of Figure 1.

Figure 3 is asection substantially on line 3- 3 of Figure 2 Figure 4 isa section on line 4-4: of Figure 3.

Eigure'5 is a perspective of the rotor shaft retaining means.

Referring by reference characters .to the drawing, numeral 7 is thecasing of the tachometer within which casing is a frame 9 carrying themechanism of the instrument. Frame 7 is secured in the casing by fourstuds designated by reference characters 10 and 10', of which studs 10are diametrically arranged vertically, and studs 10 are dia- 50 vided inthe magnet. This secondary magmetrically arranged in a horizontal line.

net is of C shape, as shown in Figure 3, its, poles lying adjacent theleft stud 10, one slightly .above and the other below the horizontalline joining the studs 10, 10'..

The .main magnet overlies the secondary magnet and isspaced therefrom.It rests on a shoulder of the frame, as is shown in Figures 2 and 4..Its gap overlies the gap of the secondary magnet,as will be seen by aninspection of Figure '1. A jewel frame 13 rests upon the main magnet 15and serves to hold it in position. The jewel frame .is a crescent shapeand is held by clamps encircling three of the studs and by nuts 22. Asshown in Figure 1,:the upper and lower studs 10 and the right hand studs10 are used to secure the crescent shape, jewel frame inposition. Acompensator o'f-kno'wn kind, and represented'by numeral 23, is arrangedto cross the poles of magnet 15 adjacent the left stud 10. It "is ofsuflicient extent to engage the two poles and is held bya clamp 20 andnut 22'. Overthe clamp and underthe nut there may be used a magneticcalibrating member 24. By suitably bending this member calibration maybe readily eifected.

The spider rotor 31 is secured to the end of rotor shaft 33, which"latter is journalled in a bore of the axial stem 35 constituting a partof the .frame 9. The rotor is shown as being located between the twomagnets. A speed-disc 18is also located between the magnets.- Itsperiphery 'is flanged as at 37 to surround the edge of the rotor. Thedisc 18 is carried bya spindle 1.7,.one end of whichis. j ournalled inthe open inner end oYf-the rotor shaft 33'. The jewe'l frame, as shownin Fig u'res 1 and 4, has a radial arm :14 bent out from the plane ofthe frame and ending in the axis of the spindle 17.. At-its end it isprovided with means to serve as a journal for the other end of:thesp'indle. The usual hair spring 23" is associated with thespindle 17and aregulat or 16. The indicator .needle is designated by .numeral 45.

To retain the rotor shaft 33 it has been the former practice to cut aslot in the stem .35 and project a disc through the slot into agrooveformedinthe shaft. As a substitute for'this arrangementthere'isused in the prescut case a retaining member 25 which is seatedin a recess in the bottom of the cup-shaped frame within the secondarymagnet. This retaining plate 25 has a slot 26 whereby the plate may beextended into an annular groove 27 of shaft 33. The plate is to beriveted to the frame as by fastening means 28. Preferably the plate 25will be so dimensioned and shaped that the fastening means 28 may passbetween the legs of the spider rotor. This is well illustrated in Figure3.

The front of the instrument is closed as usual with a dial plate, aglass and bezel.

As compared with the earlier construction where but three studs wereusedto hold the magnet in position, the present instrument is animprovement in that the magnet is held more firmly in position in itsrelation to the frame, there being four studs serving to hold themagnet, these studs being arranged at 90 intervals. Two diametricallyopposed studs are of additional length whereby these fastening studs mayalso serve to mount the instrument on its support.

The instrument in use occupies a position somewhat as in Figure 1. Informer instruments of this type the magnet gap has been in the bottom.Any displacement of the rotor shaft out of the axis, which is at rightangles to the plane of the magnet, tends to move the rotor so that itsplane is no longer parallel with the plane of the magnet. Such movement,though slight, so disturbs the operation of the instrument as to renderthe readings inaccurate. Such a tilting or displacement of the rotorshaft and rotor tends to occur, because the flexible shaft connected tothe rotor shaft 33 exerts a pulling effect, generally in a downwardlydirection. This difficulty is the greater because in previousconstructions the material cut out of the stem 35 for the reception ofthe retainer has so weakened the stem that there has been a tendency forthe stem, itself, to take a position such that its aXis is no longernormal to the plane of the magnets. By placing the gap in the horizontalaxis instead of the vertical axis any such distortion 'is rendered lessharmful. Furthermore, the feature, whereby the retaining means whichsecures the rotor shaft is so arranged as not to weaken the stem of thecasing, serves to effectively preventany such distortion of the stem ofthe frame, and in consequence of the position of the rotor shaft, androtor, therefore, remains normal to the plane of the magnets. By thesesimple and inexpensive improvements better results are secured.

Instead of constructing the jewel frame as a bridge over the hairspring, as has been done heretofore, the jewel frame is made of crescentshape with a radial arm terminating over the speed disc spindle. Thisrenders the hair spring and the parts related thereto much moreaccessible and it gives a greater range of movement for the regulator ofthe adjusting spring, as will be obvious from an inspection of Figure 1.

The added rigidity of the speed disc, accompanied by the provision ofthe flange 37, serves to prevent warping of the disc, and it alsosecures for the speed cup a more uniform magnetic drag.

I claim:

1. In a tachometer, a cup-shaped frame having an axial stem extendedhorizontally, a rotor shaft extended through said stem, a rotor carriedby and in the plane at right angles to said shaft, means to retain saidshaft comprisingia plate having a slot, said shaft having an annulargroove to cooperate with said slotted plate, and means to secure saidplate to the bottom of said cup-shaped frame over said stem.

2. The invention defined by claim 1, said rotor being of spider shape,and the retaining means being so dimensioned and shaped as to permitaccess to said fastening means between the legs of said spider rotor.

3. In combination, a cup-shaped frame having an axial stem extendedhorizontally, a rotor shaft within said stem, a magnet having polesadjacent the horizontal plane of the rotor shaft, means to secure saidmagnet to the bottom of the cup in a plane at right angles to the axisof said shaft, a second magnet in said cup parallel to and spaced fromsaid first magnet, a rotor carried by said shaft, said rotor beinglocated between said magnets in a plane parallel thereto, a crescentjewel plate overlying said second magnet, a plurality of fastening meanssecuring said jewel plate and second magnet to said frame, a speed discalso between said magnets and in a plane parallel thereto, an indicatingmeans carried by said speed disc.

4. The invention defined by claim 3 together with a retaining plate,said plate and shaft having inter-engaging parts to prevent relativeaxial movement, and means to secure said retaining plate to the bottomof said cupshaped frame.

In testimony whereof I affix my signature.

ELBRIDGE F. BACON.

